1. Field of the Invention
The present invention relates to communication navigation systems and methods, etc. for performing navigation by transmitting map data to navigation terminals via a communication network. More particularly, the invention is directed to a communication navigation system and method, etc. capable of appropriately displaying maps on the navigation terminals.
2. Description of Related Art
Various types of communication navigation systems have been proposed, which perform navigation by transmitting map data stored in a map database site, via computer and mobile communications networks including the Internet, to various types of navigation terminals, such as in-vehicle navigation units, portable navigation units, PDAs (Personal Digital Assistants) and cellular telephones, according to their request. Each of these navigation terminals presents a user with predetermined information visibly and audibly, based on position data detected by a GPS (Global Positioning System) receiver mounted thereon as well as the map data transmitted from the map database site, to guide the user to his or her destination.
In some cases, these communication navigation systems may transmit the map data at low speeds, depending upon traffic on the computer networks and how the systems are being used, for example. To display different map areas on the screen of a navigation terminal by scrolling in particular, the navigation terminal needs to receive a plurality of items of map data corresponding to these areas for quick display. To implement a satisfactory scroll-based display when the map data is transmitted at low speeds, the scroll speed must be reduced, or it may alternatively be arranged so that an area is not displayed at all unless the navigation terminal receives map data for that area within a predetermined time limit, under a fixed scroll speed. In the latter case, the user cannot, for example, check the current position, destination, etc. on the map, to his or her disadvantage.